Before you start your outline you need to have a general sense of what it is you will be arguing. If you read the source completely and take notes, your notes are probably in the same order that your thoughts occurred to you, this is fine but the objective of an outline is to arrange those thoughts in an order that will support your argument. You should then look at all the different categories and how the information you have taken in can be categorized.
Begin with the most general categories then work down to more specific. Then chose the order at which to present them.
John M 